Middle distillate fuel compositions having improved pour point characteristics



United States Patent 0.

3,087,800 MIDDLE DISTILLATE FUEL COMPOSITIONS HAVING'IMPROVED POUR POINT CHAR- ACTERISTICS Stephan Ilnyckyj and John L. Tiedje, Sarnia, Ontario, Canada, assignors to Ess'o Research and Engineering Company, a corporation of Delaware No Drawing. Filed Aug. 19, 1960, Ser. No. 50,571 3 Claims. (Cl. 44-62) The present invention relates to improving the flow at low temperatures and the pour point characteristics of middle distillates. More particularly, the present invention relates to the preparation of improved low cold test hydrocarbon fuels, in particular heating oils and diesel fuels, kerosene, aviation turbo-jet fuels and other fuels that are subject to low temperatures. In accordance with the present invention, improved middle distillate fuel compositions of improved pour points are produced by using in conjunction with middle distillates a pour depressant comprising a copolymer of ethylene and vinyl benzoate.

With the increase in the use of hydrocarbon fuels of all kinds, a serious problem has arisen in areas frequently subjected to low temperatures in the cold test characteristics of fuels. Particularly, serious problems have been encountered by heating oils and diesel and jet fuels that have too high a pour point, resulting either in distribut-ional or operating difficulties or both. For example, the distribution of heating oils by pumping or syphoning is rendered difiicult or impossible at temperatures around or below the pour point of the oil. Furthermore, the flow of the oil at such temperatures through the filters cannot be maintained, leading to the failure of the equipment to operate.

Also, the low temperature properties of petroleum distillate fuels boiling in the range between about 250 and about 800 F. have attracted increasing attention in recent years because of the growth of markets for such fuels in subarctic areas and because of the development of turbo-jet aircraft capable of operating at altitudes where temperatures of -50 F. or lower may be encountered.

It is, of course, well known to add pour depressants to lubricating oils to lower the pour point. These lube oil additives, mostly high molecular weight organic compositions formed by alkylation of benzene or naphthalene or derivatives thereof or by polymerization of lower molecular weight methacrylates, or by condensation polymerization of various kinds, are not satisfactory in service with middle distillate and lighter fuels. Poor performance of these additives might possibly result from the structural differences between waxes occurring in lubricating oils and so-called middle distillates.

A wide variety of compounds have been found to be effective as pour point depressants for lubricating oil. Among the best known are Paraflow, Santopour and Acryloid and their modifications. They are prep-ared either by condensing aromatic compounds with long chain paraffins, such as wax, or by condensing olefinic esters. It is generally considered that these pour depressants are effective in that in cooling an additivecontaining oil, the hydrocarbon chain of the additive be comes incorporated into the crystal lattice of the separated wax, while the other part of the pour depressant molecule prevents the crystals from adhering together to form a gel structure. The failure of these additives to be effective in middle distillates may at least in part be due to the basic difference in the composition between the wax in lubricating oils and that in middle distillate fuels. It is, therefore, the principal object of the present invention to set forth an improved pour depressant for 3,087,800 Patented Apr. 30, 1963 middle distillate and lighter fuels. In general, these oils boil in the range from about 250 to 750 F.

It is a still further object of the present invention to provide heating oils, diesel fuel oils, kerosenes and jet fuels having low pour points. Such fuels include aviation turbo-jet fuels, kerosenes, diesel fuels, and heating oils. Aviation turbo-jet fuels in which the polymers may be used normally boil between about 250 and about 550 F. and are used in both military and civilian aircraft. Such fuels are more fully defined by US. Military Specifications MIIrF--5624C, MILF25554A, MILF- 25558-A, and amendments thereto. Kerosenes and heating oils will normally have boiling ranges between about 300 and about 750 F. and are more fully described in ASTM Specification D-396-48T and supplements there.- to, where they are referred to as No. l and No. 2 fuel oils. Diesel fuels in which the polymers may be employed are described in detail in ASTM Specification D-975-53T and later versions of the same specification.

The polymeric pour depressants may, in accordance with the invention, be employed in conjunction with a variety of other additives commonly used in fuels such as those set forth above. Typical of such additives are rust inhibitors, anti-emulsifying agents, corrosion inhibitors, anti-oxidants, dispersants, dyes dye stabilizers, haze inhibitors, antistatic agents and the like. It will frequently be found convenient to prepare additive concentrates for use in the various types of fuels and thus add all of the additives simultaneously. Other and further objects of the present invention will appear more clearly hereinafter.

The pour depressant comprises a particular copolymer of ethylene and vinyl benzoate. It is preferred that the mol. percent of ethylene in the copolymer be in the range from about 93-88% as compared to the mol. percent of vinyl benzoate in the range from about 7 to about 12%. A very desirable ethylene-vinyl benzoate copolymer contains about 10 mol. percent of vinyl benzoate.

The molecular weights of the ethylene-vinyl benzoate copolymer are critical and should be in the range from about 800 to 1400, preferably about 1200. The molecular weights are determined by K. Rasts method (Ber. 55, 1051, 3727 (1922)).

The ethylene-vinyl benzoate copolymer as described above is used in a concentration in the range from about .002 to .l% by weight, preferably in the concentration in the range from about .01 to .05% by weight.

Surprisingly, these low molecular weight copolymers have no effect upon the pour points of lubricating oils, thus emphasizing the difference in structure betweerrthe wax associated on the one hand with lube oils and on the other with middle distillates. The low molecular weight copolymers may be prepared by any peroxide process. In some instances, it may be desirable to first prepare a higher average molecular weight oopolymerization product and then recover from that product material having a molecular weight within the range between about 800 and about 1400. Since such copolymerization products normally consist of a smear of copolymers whose molecular weights vary over a wide range, an effective method for recovering for example the 1200 molecular weight portion therefrom is to extract the product with a solvent such as normal heptane or methyl ethyl ketone. Other methods for obtaining the low molecular weight materials include thermal degradation of the high molecular weight polymer or treatment of the high molecular weight copolymer with ozone in order to break the polymer chains. Still other methods also useful will be apparent to those skilled in the art.

A very desirable method is to conduct copolymerization in a benzene solution using ditertiary butyl peroxide as an initiator at a temperature in the range from about 260 to 400 F. The preferred temperature is in the range from 290 F. to 325 F. as for example about 300 F. The pressure is in the range from about 600 to 1500 pounds, preferably, at about 900 pounds. The autoclave or similar equipment containing the solvent, initiator and vinyl benzoate is purged about three times with nitrogen, twice with ethylene and then charged with a sufiicient amount of ethylene to yield the desired pressure when heated to the reaction temperature. During the copolymerization, additional ethylene is added whenever the pressure drops by about 100 p.s.i.g. Copolymerization is considered complete when it is less than 50 p.s.i.g. pressure drop per hour. The product is stripped free of solid and unreacted vinyl benzoate under vacuum.

One specific method of manufacturing the pour depressant of the present invention is as follows: Add 400 milliliters of benzene into the reactor, then heat to about 300 F. and pressure to 900 pounds with ethylene.

Then add the vinyl benzoate diluted with 150 milliliters of benzene and also add milliliters of ditertiary butyl peroxide diluted with 105 milliliters of benzene.

The vinyl benzoate is added uniformly over two hours whereas the ditertiary butyl peroxide is added uniformly over three hours.

After the reactants have been added, including the catalyst, heat soaked for about one-half hour and allow the mixture to cool thereafter to 150 F. This temperature is below the boiling point of benzene. Remove the product and then strip off the benzene.

A typical distillate fuel boiling in the range from 250 to 750 F. to which the present additives may be added are middle distillate heating oils. These fuels are of commercial grade and have typical properties as follows:

Composition:

Straight run gas oil wt. percent" 50 Cat. cracked gas oil wt. percent 50 Inspections:

Gravity, API 29.1 ASTM pour, F., no additive Flash, Pensky-Martin, F 192 Distillation, ASTM, F.

IBP 398 10% 492 50% 566 90% 612 FBP 644 The improvements obtained by adding the additives in accordance with the present invention are set forth in the following table. All pour points quoted hereafter were obtained by ASTM Method D-97-47.

A number of tests were conducted using various copolymers in a 50-50 blend of virgin gas oil and cracked gas oil. The virgin gas oil boiled in the range from about 350 to 700 F, and the cracked gas oil boiled in the range from about 350 to 650 F. The blend had a pour of 20 F. The various copolymers were prepared under varying pressure and other varying operating conditions. As pointed out heretofore, the critical factors with respect to desirable copolymers are molecular weights and the concentration of the vinyl benzoate in the copolymer. The results of these tests are shown in the following table:

TABLE Synthesis and Pour Depressing Potency of Copolymers 0f Ethylene With Vinyl Benzoate [Conditions of Copolymerization: 900 p.s.i.g., 300 F., one gallon reactor] Operation A B Benzene, ml 055 455 Vinyl Benzoate, g. 241 277 Vinyl Bcnzoate, g /mi 2.0 2. 3 D1 t butylperoxide, g. 11.9 11.9 Di-t-butylpcroxide, g./min 0. 066 0. 006 Copolymcrization Time, Hr 3. 5 3. 5 Product:

Yield, g 475 438 Copolymer, gJPeroxide, g 39. 9 36. 8

Vinyl Benzoate, Wt. Percent 30. 9 40. 7

Vinyl Benzoate. Mol. Percent 10.0 14. 2

Molecular Weight 1, 250 1,480 ASTM Pour Point 1 F.:

0.015 Wt. Percent Copolymer +5 +15 0.025 Wt. Percent Copolymer 20 +15 1 Reference oil: 50/50 blend ofstraight run and cracked gas oils, ASTM from +20 F.

From the above, it is apparent that the copolymer is excellent providing the molecular weight as well as the amount of the vinyl ester in the copolymer are in the desired range. It is to be noted that if the concentration of the vinyl ester approaches 15 mol percent, the effectiveness of the compound is materially reduced. On the other hand, if the mol. percent of the ester in the copolymer is about 10% with the molecular weight of around 1200, its pour depressant ability is appreciable.

What is claimed is:

1. A petroleum distillate fuel boiling in the range from about 250 F. and about 750 F. which has been improved with respect to the pour point by the incorporation thereof of from about .002 to .l% by weight of an oil soluble copolymer having a molecular weight in the range of about 800 to 1400, said copolymer being a copolymer of ethylene and from about 7 to 12 mol percent of vinyl benzoate.

2. The fuel composition as defined by claim 1 wherein the molecular weight of the copolymer is about 1200 and wherein the mol. percent of the vinyl benzoate present is about 10%.

' 3. The fuel composition as defined by claim 2 wherein the concentration of the copolymer is in the range from about .01 to .05% by weight.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PETROLEUM DISTILLATE FUEL BOILING IN THE RANGE FROM ABOUT 250*F. AND ABOUT 750*F. WHICH HAS BEEN IMPROVED WITH RESPECT TO THE POUR POINT BY THE INCORPORATION THEREOF OF FROM ABOUT .002 TO .1% BY WEIGHT OF AN OIL SOLUBLE COPOLYMER HAVING A MOLECULAR WEIGHT IN THE RANGE OF ABOUT 800 TO 1400, SAID COPOLYMER BEING A COPOLYMER OF ETHYLENE AND FROM ABOUT 7 TO 12 MOL PERCENT O VINYL BENZOATE. 